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AmigaOS 4 only runs on PowerPC CPUs, but was largely based on AmigaOS 3.1 source code which only ran on 68k CPUs. So the code base has already been ported from one architecture to another. The difficulties in porting would probably come from endian issues and the almost complete lack of any Amiga-compatible hardware devices on any existing computers using x86 and ARM CPUs. However regardless of the difficulties it would be possible, just unlikely that anyone would consider it practical. In any case, I'm not sure if this question is on-topic here.
– Ross RidgeSep 30 '17 at 16:46

Since an x86 (or ARM) machien is turing complete, every port from any other machine is possible. Isn't it? as @RossRidge already mentioned, the question in't on topic, nor does it make much sense, or useful. I also see no way to make it more specific to be answered beside above platitude.
– RaffzahnSep 30 '17 at 18:25

Would the expert opinion "quite hard, but not excessively hard" be acceptable? Even though I don't think that the question is off-topic, it is unclear what you're asking, and the answers would be opinion based.
– Leo B.Sep 30 '17 at 19:03

2 Answers
2

AROS is an existing reimplementation of AmigaOS 3.1 with cross-platform compatibility (current distributions run on MC68020, PPC and x86 platforms; given the diversity of these platforms I would presume adding ARM compatibility would be fairly simple). While its developers have stated they have no desire to implement the updates that were included in the more recent AmigaOS 4 release, it would serve as a useful base for a fork.

Wikipedia has a list of the most major changes in AmigaOS 4. There's nothing here that's Earth-shatteringly difficult. As OS development tasks go, it's not trivially easy but it isn't really hard either. Of course, working on an OS is never quite as simple as working on standard applications, as you have to either deal with emulated hardware or running on a system that may not have a functioning OS while you test it. I reckon a small team with people with experience in the relevant fields (low level hardware interfacing, on-disk data structures, UI and graphics development) could do it in about a year. So from a technical perspective, I'd say it's clearly achievable.

But then, the AmigaOne platform and consequently AmigaOS 4 were commercial failures, so the need for such a system doesn't seem to be there otherwise it wouldn't have failed. So finding a team motivated to spend the time to make these changes would be tricky. As would getting funding to pay such a team. So from a practical perspective, I don't imagine it will ever happen.

In addition to Jules's AROS reference: given the functionality of both x86 and ARM platforms and AmigaOS 4's hardware requirements, it's definitely possible.

However, for a native platform port you not only need to make the bare OS run on the hardware, you also need to provide drivers for the pool of hardware you need to work. With AmigaOS's hands-on approach, writing the code isn't very hard but nowadays, getting to the hardware details is - there's only few hardware around where sufficient hardware documentation is provided.

All in all, the difficulty isn't very high if you're able to stick to hardware that's well documented. Nonetheless, you're looking at several developer years of work.